1. Field of the Invention
The present invention relates to an optical disc drive, and more particularly to an optical disc drive adapted to write data to, and/or read data from, optical discs being different in format from each other, such as a compact disc (CD), digital video disc or digital versatile disc (DVD), etc. According to the present invention, a plurality of light sources is disposed apart from each other radially of such an optical disc and a laser light is emitted from one of the light sources selected according to the type of optical disc loaded in the optical disc drive towards the optical disc and focused through a common optical system for the different types of optical discs. Thus, a single optical pickup can be used in common with such a plurality of optical discs without any deterioration of the optical property.
2. Description of the Related Art
The conventional optical disc drive or CD player is adapted to irradiate a laser beam from an optical pickup onto an information recording surface of a CD and process a detection result of a return light from the CD surface to read or reproduce a variety of data recorded in the CD.
The conventional optical pickups include a type having a light source and photodetector disposed separately therein, and a type using an optical integrated device consisting integrally of a light source and photodetector. The U.S. Pat. Nos. 4,873,429 and 4,733,067 disclose examples of the construction of the optical pickups of the latter type. This type of optical pickup can be designed more compact and have a higher reliability.
It is considered that using such an optical integrated device to build the optical pickup also in an optical disc drive for DVD, a so-called DVD player, for example, the DVD player can be designed compact and simple. A DVD player designed to write data to, and/or read data from, a CD as well will be very conveniently usable.
In this case, by forming an optical integrated device integrally from a light source and photodetector for DVD and a light source and photodetector for CD, an optical disc player capable of writing data to, and/or reading data from, both CD and DVD can be provided.
When the optical integrated device is constructed as in the above and an objective lens is commonly used with both DVD and CD, either of the light source for DVD or that for CD will be disposed off the optical axis of the objective lens. The laser beam emitted from the light source thus disposed off the optical axis will be incident obliquely to the objective lens. As a result, the obliquely incident laser beam will have an increased aberration and thus the optical property will be deteriorated.
As defined in the standard, the pit depth in the compact disc (CD) is one eighth (λ/8) of the wavelength λ of the laser beam irradiated to the CD, while the pit depth in the DVD is one fourth (λ/4) of the wavelength λ of the laser beam irradiated to the DVD. Thus, in the DVD player, it is difficult to detect a tracking error signal by the similar method to that for CD. Namely, tracking error signal has to be produced by the so-called differential phase detection (DPD) method, for example. In this DPD method, the laser diode as light source has to be disposed in such a manner that the deflection plane of the laser beam will be parallel or perpendicular to the scanning direction of the laser beam.
For effective utilization of the internal space of the optical integrated device, the laser diode should desirably be disposed in such a manner that the deflection plane of the laser beam will be parallel or perpendicular to the direction of the optical path of the laser beam.
However, when the laser beam deflection plane is directed as in the above, the optical property of a read signal from the optical disc will be deteriorated.